Pressure-electric transducers



Nov. 3, 1964 A, J. HILGERT PRESSURE-ELECTRIC TRANSDUCERS Filed Jan. 24, 1962 INVENTOR. ADOLPH J- HILGERT ATTORNEYS.

United States -Patent C 3,155,896 PRESSURE-ELECTRIC TRANSDUCERS Adolph J. Hilgert, Milwaukee, Wis., assigner to .'iohnson Service Company, Milwaukee, Wis., a corporation of Wisconsin Filed Jan. 24, 1962, Ser. No. 168,386 6 Claims. (Cl. 323-95) This invention relates to improvements in pressureelectric transducers.

There are many applications involving the use of electrical devices such as indicators or electric controls, in such fields as heating, Ventilating or air conditioning, where it would be desirable to have the electrical characteristics of the device modified in response to pressure. Heretofore this has been accomplished by the use of piezo electric devices, inductance, capacitance or resistance change. Generally, however, the changes produced by such means are of such a low power level that some amplification of the change is required to make it useful for indicating or for control purposes.

It is a general object of the present invention to provide a pressure-electric transducer which has high efficiency, there being a power unit which allows negative feedback to be used, thereby resulting in an output which is substantially independent of supply voltage and load variations.

A further object of the invention is to provide a device as above described wherein the impedance of the power unit can be changed to allow changes in the output voltage range.

A further object of the invention is to provide a pressure-electric transducer which includes a novel combination with a pressure sensitive contact device such that the pressure resistance characteristics of the combination can be changed to fit various applications whereby it is able to handle useful power without further amplification.

Other objects of the invention are to provide a pressureelectric transducer which is relatively simple in design, inexpensive to. manufacture, which has high sensitivity, and which has low power requirements.

With the above and other objects in view, the invention consists `of the improved pressure-electric transducer and all of its parts and combinations, as set forth in the claims, and all equivalents thereof.

In the accompanying drawing, illustrating one complete embodiment of the preferred form of the invention, in which the same reference numerals designate the same parts in all of the views:

FIG. l is a longitudinal vertical section through the improved transducer;

FIG. 2 is a top view of the transducer with the cover removed; FIG. 3 is a partially diagrammatic view showing the power unit and circuit, the power unit being shownvas it would appear if a transverse section through the device of FIG. l were taken;

FIG. 4 is an enlarged vertical sectional View of the improved pressure-responsive contacts in a relatively open position;

FIG. 5 is a view of the contacts in a relatively closed condition; and

FIG. 6 is a view similar to FIG. 4 showing modified contacts.

Referring more particularly to the drawing, the numeral 10 designates a suitable housing havinga removable cover 11. Suitably supported in spaced position above the bottom of the housing is an inner frame l2 having spaced, opstanding legs 13 at one end. Mounted on the base portion 12 is a bellows connector 15 supporting an expansible inherently resilient bellows 15 which is connected by a suitable air line 16 to an inlet fitting 17 at one end of the casing. Variations in pressure, constituting the signal from an external sourcev such as a pneumatic thermostat, is admitted to the bellows through the inlet fitting 17.

Projecting upwardly from the top of a rotatable bellows cap 18 is a set point adjustment screw 18 which is threaded through a threaded opening 19 in a transfer lever 20, there being a friction spring 9 looped around the screw to hold it in set position. The lower end of the bellows unit has a `depending threaded stem 21 projecting through an opening 22 in the inner frame 12, there being a nut 23 threaded on the lower end of the stem 21. The arrangement at the top is such that through manipulation of the set point adjustment screw 18 the distance of the top of the bellows from the transfer lever may be varied, the cap 18 rotating around the top of the bellows when the screw 18 is turned.

The transfer lever Ztl is suitably supported on L-shaped metal flexure hinges 24, the latter being suitably supported on portions of the end legs 13 of the interior frame. One end of the transfer lever has counterweights 25 suitably connected thereto, as shown. The other end of the transfer lever has an armature 26 supported on its under face, which armature coacts with a feedback power unit 27, the latter (which will be later described in greater detal) including suitable windings 28.

An S-bracket 29 has an upper portion secured to the upper face of the transfer lever above the armature, has a downwardly projecting portion and an outwardly projecting shelf portion 30 carrying an insulator sleeve 31 for a lower Contact 32.

Projecting upwardly from the end of the interior support 12, which is opposite the bellows, is a bracket 33 having an inwardly hanged upper end 34 which supports an insulator 35. An upper contact member 36 has an upwardly projecting threaded stern 40 lthreaded into a headed nut 37 which is slidable in the insulator 35. A spring 3d is suitably supported between a spring seat 39 and the insulator to urge the upper contact in a downward direction with the head of the nut forming a stop. The arrangement is such that the threaded stem forms a range adjustment screw and may be manipulated to vary the normal spacing between the armature 29 and pole faces of the power unit 27.

Referring to FIGS. 4 and 5, -the adjacent ends of the Contact members 32 and 36 are encased within a damping sleeve of rubber or rubber-like synthetic material 41 such as Viton The upper end of the sleeve is bonded to the contact member 36 and the lower end of the sleeve is bonded to the contact member 32. Between the ends of the contact members is a chamber containing an electrical conducting material 42, which may be powdered graphite, carbon or metal mixed with a viscous, electrically nonconducting material, or the chamber may contain an electrolite. The exact amount of conducting material may be varied. However, it should be varied so that for any gap, such as the gap shown in FG. 4 between the ends of the conductors, the mixture has a very high electrical resistance. ln FIG. 4 the gap is shown when the armature 26 is in the down position of FIG. l before any upward pressure has been applied. In FIG. 5 the gap is shown after the application of pressure where the gap at 42 is materially reduced, with the excess material being squeezed radially outwardly from the gap into the extra space created at the sides by the bulging 43 of the flexible sleeve 41. When the pressure on the upper contact is relieved the resiliency of the rubber sleeve 41 tends to return itself to the straight condition of FIG. 4 and acts to force the powdered mixture back into the gap, as in FIG. 4.

The voltage supply from a suitable source of direct current is conducted by the supply wires 44 and 45. Wire lift of the lower contact member 32.

'44 is electrically connected to the upper contact 36. The -`wire 45 is electrically connected to one terminal of the `windings 2S. The other terminal 46 of the windings is 'connected to the lower contact 32. Another wire 47 is connected to said terminal 46 of the windings through the lower Contact 32. lf desired, there may also be a capacitor dit connected between the upper and lower contacts to suppress arcing. lt is preferred to have the supply voltage approximately 4 volts DC. maximum, as higher voltages cause unstable operation. The voltage output is carried from opposite sides of the coil 28 by the conductors 45 and 47.

In the modified arrangement of FiG. 6, instead of using the mixture of powdered conducting material and viscous material at 42 as in FIG. 4, there is bonded to the lower end of the contact member 36 a carbon disc 52 and there is also bonded to the upper end of the contact member 52 a carbon disc 53. `A damping sleeve 41 is used just as in FIG. 4. With the arrangement of FIG. 6, when no pressure is being applied to the contacts, the carbon discs 52 and 53 are either barely in contact or very slightly separated so that there is high resistance to ilow of electricity. When pressure is applied, however, to the carbon discs, their resistance to the flow of current decreases proportionately to the amount of pressure so that the net result is the same as in the construction of FIGS. 4 and 5.

In FIG. l, the armature 26 is shown in Contact with the pole face enlargements 43 at the top of the power unit. in normal use, however, there is a small air gap (.002- .0l) between the faces of the armature and the pole face enlargements 48.

The power unit 27 is of novel design for this purpose and includes an electromagnet having cores 49 with the upper pole face enlargements 48 heretofore referred to, and with lower pole face enlargements 43', the coils 28 being wound on the cores as shown in FIG. 3. Located near the air gap 5@ is a polarizing or biasing permanent magnet El. This produces a magnetic flux distribution as shown at (a) and (b) in FIG. 3, this being an initial flux which is present without any signal occurring, flux (b) partially saturating its iron path, thereby causing llux to ow in path (a). A further advantage for the power unit of FIG. 3 is that if the current in the coils is such that the flux in the air` gap is increased, the ilux (b) in the core is decreased by approximately the same amount. This means that the cores may be made smaller, making more space available for the coils for compactness. The polarization illustrated in FIG. 3 increases the sensitivity of the electromagnet. Furthermore, the greater amount of initial lux produces a more sensitive device, which is important.

Operation l'n operation, the supply voltageA from the conductors and 45'is across the series-connected contacts and coils 2S of the power unit 537. These coils ma however, be connected in parallel. When air or other liuid pressure is applied through the tting l? and tube 16 into the in- `design which includes a hinge angle ofrslightly less than 90. Through the S-bracket 2,9, this causes an' upward This tends to compress the powdered material 42 between the contacts or the carbon discs 52 and 53 of FIG. 6 to a greater or lesser degree, depending upon the pneumatic force exerted, and causes current toV llow through the windings 2S of the power unit. However, as soon. as current flows through the power unit there is a pull in a downward direction on the armature 26 which tends to spread the contacts 32 and 36, this action being in the nature of a negative feedl back. Thus, there is a force balance established between the action of the bellows and the power unit 27. The higher the input force of the compressed air into the bellows, the greater the amount of current which flows through the coils 2S and, therefore, the higher the output voltage from the conductors 45 and 47.

The, sley ve 41 acts as a holding member to keep the contacts 3d and 32 in alignment and from separating under shock and vibration. lt is preferred to employ carbon for the material at 42 to give a more gradual change of contact resistance with pressure. Most conductors have too great a change of resistance with pressure -to permit stable operation of the transducer. It is preferred to have the 'l resistance of the coils 2S approximately 350 ohms. The

range adjusting screw itl changes the length of the gap at 42 between the contact members 32 and 36 which, in turn, changes the value 'of the feedback force transmitted through the power unit to the transfer lever 20. The set point adjusting screw 18 changes the force on the transfer lever due to the upward spring action of the bellows. The initial spring force of the bellows is usually set to balance out the pull from the power unit produced by the permanent magnet of the power unit so that the output signal is 0 for t) input pressure.

From the above it is apparent that the device has high etliciency because of the particular design, includingl the power unit 27 which allows negative feedback to be used, resulting in an output through the conductors 45 and'47 which is substantially independent of supply voltage and load variations. Since little motion takes place, the initial sensitivity is extremely high, so that enough feedback can be used to produce stable operation. lt is also clear that changes in the output voltage range may be made by changes in the impedance of the power unit. In addition, the pressure-resistance relationship in the Contact unit shown in FIGS. 4 and 5 may be changed by varying the proportion of the conducting to non-conducting ingredients at 42, by varying the area of the ends of the contact members 32 and 36, or by changing the shape of the contacting surfaces of one or both of theends of the contact members 32 and 36 such `as by having a convex face for one or both of said members to increase the effective size of the gap or by changing the type of contacting material used, as in FIG. 6.

Various changes and modifications may be made'without kdeparting from the spirit of the invention, and all of such changes are contemplated as may come within the scope of the claims.

VWhat I claim is:

1. A system for producing an output voltage which is substantially independent of supply voltage and load Variations comprising ia pressureelectric transducer having a frame, an electrical suply circuit, a transfer lever pivoted to said frame, pressure-responsive means for pivotally moving said transfer lever in a first direction, electric contact means in said electrical supply circuit connectedwith said transfer lever and having pressure variable conducting means therebetween responsive to movement of said transfer 'lever for controlling the ow of electricity in said supply circuit in accordance with lever movement, magnetic feedback means in saidsupply circuit for moving said transfer lever reversely from said first direction of movement, said magnetic feedback means including av coil in the supply'circuit, and electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change in said pressure-responsive means and substantially independent of supply voltage and load variations.

2. A system for producing an output voltage whichis Y substantially independent of supply voltageV and load variations comprisinga pressure-electric transducer having `a frame, an electrical supply circuit, a transfer lever pivoted to said frame, a pressure-,responsive actuator for pivotally moving said transfer lever in a iirst direction, pressureresponsive electric 'resistance means inlsaid electrical supply circuit connected with and responsivejto movement of said transfer lever for controlling the liow of electricity in said supply circuit in accordance with pressure change transmitted by said lever movement from said actuator, magnetic feedback means in said supply circuit for moving said transfer lever reversely from said first direction of movement, said magnetic feedback means including a coil in the supply circuit, and electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change from said pressure-responsive actuator and substantially independent of supply voltage and load variations.

3. A pressure-electric transducer comprising a frame, an electrical supply circuit, a transfer lever pivoted to said frame, a pressure-responsive actuator for pivotally moving said transfer lever in a first direction, pressureresponsive electric resistance means in said electrical supply circuit connected with and responsive to movement of said transfer lever for controlling the iiow of electricity in said supply circuit in accordance with pressure changes transmitted by said lever movement from said actuator, magnetic feedback means in said supply circuit for moving said transfer lever reversely from said first direction of movement, said magnetic feedback means including a coil in the supply circuit, and electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change from said pressure-responsive actuator and substantially independent of supply voltage and load variations, said pressureresponsive electric resistance means comprising cooperating contacts, one of which is connected to said lever for movement relative to the other contact when said lever is moved, a pressure variable conducting means between said contacts, and a resilient damping sleeve connected between said contacts and confining said pressure-variable conducting means.

4. A pressure-electric transducer comprising a frame, an electrical supply circuit, a transfer lever pivoted to said frame, a pressure-responsive actuator for pivotally moving said transfer lever in a first direction, pressureresponsive electric resistance means in said electrical supply circuit connected with and responsive to movement of said transfer lever for controlling the ow of electricity in said supply circuit in accordance with pressure changes transmitted by said lever movement from said actuator, magnetic feedback means in said supply circuit for moving said transfer lever reversely from said first direction of movement, said magnetic feedback means including a coil in the supply circuit, electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change from said pressure-responsive actuator and substantially independent of supply voltage and load variations, said pressure-responsive electric resistance means comprising cooperating contacts, one of which is connected to said lever for movement relative to the other contact when the lever is moved, la pressure-variable conducting means between said contacts consisting of a viscous non-conducting material mixed with a conducting powder, and a resilient damping sleeve connected between said contacts and confining said pressure-variable conducting means.

5. A pressure-electric transducer comprising a frame, an electrical supply circuit, a transfer lever pivoted to said frame, a pressure-responsive actuator for pivotally moving said transfer lever in -a first direction, pressureresponsive electric resistance means in said electrical supply circuit connected with and responsive to movement of said transfer lever for controlling the flow of electricity in said supply circuit in accordance with pressure changes transmitted by said lever movement from said actuator, magnetic feedback means in said supply circuit for moving said transfer lever reversely from said irst direction of movement, said magnetic feedback means including a coil in the supply circuit, electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change from said pressure-responsive actuator and substantially independent of supply voltage and load variations, said pressureresponsive electric resistance means comprising cooperating contacts, one of which is connected to said lever for movement relative to the other contact when the lever is moved, a pressure-variable conducting means between said contacts which consists of a carbon disc bonded to one contact and a carbon disc bonded to the other contact, and a resilient damping sleeve between said contacts and confining said carbon discs.

6. A pressure-electric transducer comprising a frame, an electrical supply circuit, a -transfer lever pivoted to said frame, a pressure-responsive actuator for pivotally moving said transfer lever in a rst direction, electric contact means in said electric supply circuit connetced with and responsive to pressure changes transmitted by movement of said transfer lever for controlling said electrical supply circuit, magnetic feedback means including a coil in said supply circuit for moving said transfer lever reversely from said first direction, electrical output conductors leading from opposite sides of said coil whereby the electrical output is proportional to pressure change from said actuator .and substantially independent of supply voltage and load variations, said magnetic feedback means including an armature on said transfer lever and including an electromagnet supported on said frame and having core portions for said coil with pole faces positioned for coaction with said armature and normally separated by an air gap therefrom, and a polarizing permanent magnet adjacent said electromagnet located to produce an initial magnetic iiux across the air gap between the armature and pole faces of the electromagnet core, and so located that the electromagnetic coil causes said iluX to be shifted between the core portions of said electromagnet and the air gap in amounts depending upon the flow of current through the coils.

References Cited in the tile of this patent UNITED STATES PATENTS 1,953,819 Payne Apr. 3, 1934 2,435,425 Cunningham Feb. 3, 1948 2,822,452 Neild Feb, 4, 1958 2,959,219 Hajny Nov. 8, 1960 

1. A SYSTEM FOR PRODUCING AN OUTPUT VOLTAGE WHICH IS SUBSTANTIALLY INDEPENDENT OF SUPPLY VOLTAGE AND LOAD VARIATIONS COMPRISING A PRESSURE-ELECTRIC TRANSDUCER HAVING A FRAME, AN ELECTRICAL SUPLY CIRCUIT, A TRANSFER LEVER PIVOTED TO SAID FRAME, PRESSURE-RESPONSIVE MEANS FOR PIVOTALLY MOVING SAID TRANSFER LEVER IN A FIRST DIRECTION, ELECTRIC CONTACT MEANS IN SAID ELECTRICAL SUPPLY CIRCUIT CONNECTED WITH SAID TRANSFER LEVER AND HAVING PRESSURE VARIABLE CONDUCTING MEANS THEREBETWEEN RESPONSIVE MOVEMENT OF SAID TRANSFER LEVER FOR CONTROLLING THE FLOW 